Residual current devices, which are also referred to as ground fault circuit interrupters (GFCIs), have been in use worldwide for over forty years, and these devices have contributed significantly to the reduction in fatal accidents arising from electric shock. The principle of operation of RCDs will be well known to those versed in the art, but detailed information can be found in the article “Demystifying RCDs”, at www.rcd.ie, which is incorporated herein by reference in its entirety.
RCDs are fitted with a test button to enable the user to verify the correct operation of the device, but users cannot be relied upon to carry out such testing. Furthermore, such testing may be carried out at intervals of many months, and a faulty device could therefore go undetected for long periods during which time the RCD may be required to operate and may not be able to do so.